Pressure vessels having an internal piston are in widespread use to actuate other implements or devices. Sometimes these pressure vessels are referred to as actuators. The applications of such pressure vessels are virtually limitless, and the size and shape of such pressure vessels, as well as the devices actuated by the pressure vessels, are relatively unconstrained. Hydraulic cylinders are one commonly used form of pressure vessel. Hydraulic cylinders are often used as actuators to control the movement of mechanical devices, such as a loader arms, buckets, and claws, on construction equipment. Other forms of pressure vessels include pneumatic cylinders and accumulators.
Accumulators have been used in power fluid systems to store potential energy for later use. While accumulators utilize a piston therein, they often do not include a piston rod extending from the piston to outside of the pressure vessel. Instead, accumulators often include a hydraulic fluid on one side of the piston and a compressible material, such as a gas, on the other side of the piston. Monitoring the position of a piston in an accumulator provides feedback on the stored potential energy available in the accumulator. Not knowing the amount of stored energy remaining in an accumulator represents a safety concern.
In many pressure vessels that utilize a piston that moves within the pressure vessel, there is a need for greater control of the movement of the device imparted by the actuator. Numerous designs are available for detecting the position of a piston rod extending out of a hydraulic cylinder or a pneumatic cylinder in order to detect the location of the piston within the hydraulic cylinder or the pneumatic cylinder. For example, see U.S. Pat. Nos. 8,482,607 and 6,834,574. In the case of an accumulator, where there is no piston rod extending outside of the pressure vessel, such designs would not be useful for determining the location of the piston within the pressure vessel.
Various alternative techniques are provided for sensing the position of a piston within a hydraulic cylinder. Certain alternative techniques provide for placing electronic equipment within the high pressure environment inside a cylinder. Exemplary disclosures include U.S. Pat. Nos. 5,182,980, 5,856,745, 6,234,061, 6,484,620, 6,769,349, 7,716,831, 7,180,053, and U.S. Patent Publication No. 2015/0096440.
Improvements in the design of pressure vessel arrangements and pressure vessels that permit the detection of the location of a piston within a pressure vessel are desired. In particular, designs that do not require monitoring the position of a piston rod or placing electronic equipment inside the high pressure environment inside a pressure vessel are desired.